1. Field of the Invention
This invention relates to a technique for learning a stability factor of a vehicle.
2. Description of the Related Art
Techniques are known which use a stability factor of an automobile (hereinafter referred to as vehicle) in order to control the vehicle upon traveling of the vehicle.
For example, as a technique for controlling the posture of a vehicle upon turning, braking force is applied to a particular wheel or wheels upon turning to control a steering characteristic (yaw moment) of the vehicle to correct the posture of the vehicle upon turning with respect to the turning direction to achieve traveling stability of the vehicle (refer to, for example, Japanese Patent No. 3,257,354 (hereinafter referred to as Document 1)).
According to the technique disclosed in Document 1, yaw moment control is carried out in response to the deviation between a target yaw rate calculated using a standard two-wheeled model and an actual yaw rate detected by a sensor. For the calculation of the target yaw rate YA, a stability factor A indicative of the steering characteristic of the vehicle is used as in the following expression:YA=LPF2[LPF1{Vb/(1+A×Vb2)×(δ/L)}]where LPF1 and LPF2 represent low-pass filter processes, and Vb represents the vehicle speed, δ the steering angle, and L the wheel base.
Incidentally, for the stability factor for use for control of a vehicle beginning with such posture control of a vehicle as described above, usually a fixed value suitable for the vehicle is used. In particular, a steady traveling test or the like is performed, and a stability factor A is calculated from a vehicle speed V, a steering angle δ and a yaw rate ω obtained then. Then, for the same vehicle model, the calculated stability factor A of a fixed value is used to perform control.
However, the stability factor of a vehicle varies depending upon the state of the vehicle (for example, the position of the center of gravity, tyres, the rigidity of the vehicle and so forth). Therefore, where a fixed value is used as described above, it is sometimes impossible to perform appropriate control for the vehicle suitable for various situations of the vehicle. This is a significant subject particularly with commercial vehicles such as trucks and vans with which the load situation varies significantly and buses and so forth on which a great number of people get.